This node group takes roughness into account when calculating Fresnel.
The group also has enhancements for roughness and color.
Grazing Reflectivity: This produces realistic reflections at grazing angles. The Grazing Reflectivity parameter controls the strength. The GR Falloff parameter extends the reflections.
Color Correction: This addresses an issue that causes color to appear too dark at grazing angles.
The group is compatible with 2.79 and 2.8.